In situ sediment dispersion estimates in the presence of discrete layers and gradients

Charles W. Holland, Jan Dettmer

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

One of the difficulties in validating sediment models has been the lack of reliable low frequency dispersion measurements. A reflection method is presented that yields in situ dispersion without sediment disturbance over a broad range of frequencies and can explicitly disentangle frequency-dependent effects of vertical structure, e.g., layers and gradients. Measurements on the outer shelf from 300 to 3000 Hz show that dispersion is a strong function of depth in the sediment column. The depth and frequency-dependent results generally agree well with independent measurements on core data. Cohesive sediments in the upper few meters exhibit a nearly frequency-independent sound speed and a nearly linear frequency dependence of attenuation. In the lower part of the sediment column the sediments are more granular: the lowest layer exhibits an attenuation with a peak frequency at 1100 Hz, where its dependence below and above trends to f2 and f1/2, respectively. While Biot theory predicts this dependence, its underlying physical explanation, fluid flow through interstitial pores, does not seem plausible for this sediment due to the unreasonable permeability value required. Viscous grain shearing theory also predicts this dependence, but it is not known whether the parameter values are reasonable.

Original languageEnglish (US)
Pages (from-to)50-61
Number of pages12
JournalJournal of the Acoustical Society of America
Volume133
Issue number1
DOIs
StatePublished - Jan 1 2013

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sediments
gradients
estimates
attenuation
In Situ
Sediment
Layer
shelves
shearing
fluid flow
permeability
interstitials
disturbances
low frequencies
porosity
trends
acoustics
Attenuation

All Science Journal Classification (ASJC) codes

  • Arts and Humanities (miscellaneous)
  • Acoustics and Ultrasonics

Cite this

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In situ sediment dispersion estimates in the presence of discrete layers and gradients. / Holland, Charles W.; Dettmer, Jan.

In: Journal of the Acoustical Society of America, Vol. 133, No. 1, 01.01.2013, p. 50-61.

Research output: Contribution to journalArticle

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